If you have a gas central heating system installed it must be one of the following.


Also known as conventional or regular boilers. Their sole purpose is to generate heat only. For heating and hot water circulation there is an external pump and usually a 3 port (diverter valve). These components and the hot water tank are usually located in the airing cupboard. The boiler is fitted on its own into a different location.

  • system components spread throughout the property
  • heat only boilers have only a few moving parts therefore last a lot longer than system or combi boilers


This type of boiler not only generates the heat but circulates the water as well. You still have the 3 port valve externally. The pump is built in. That is the major difference compared to the heat only boiler. There is still a hot water cylinder.

  • system components spread throughout the property
  • system boilers have relatively small amount of moving parts compared to combi boilers, they are sort of between combi and heat only boilers in terms of complexity


Combi boilers generate, circulate, and divert heat between hot water and heating modes. There is no hot water tank needed as the hot water generated on demand as we open the hot tap.

  • all the system components located inside this boiler therefore it is a very good space saver. No need for hot water storage, pump, valves and programmers etc...
  • combi boilers are very complex so if they break down usually it is more expensive to fix them